High-Frequency Oscillations Not a Good Predictor of Outcomes After Epilepsy Surgery

HFOs were predictors of good or poor surgical outcome in 69.2% of patients, resulting in a modest validation of the researchers’ hypothesis.

Results of a multicenter study published in Neurology demonstrate that interictal high-frequency oscillations (HFOs) are not the strongest predictors for postsurgical outcome in patients undergoing epilepsy surgery.

Up to 20 consecutive patients with epilepsy from each of the following centers were included in the study: the Montreal Neurologic Institute, the Epilepsy Center Freiburg, and the Pediatric Epilepsy Program of the University of California Los Angeles. Patients were enrolled if they had received intraoperative or chronic intracranial electrocorticography (EEG) and subsequent surgical resection.

The study investigators hypothesized that surgical planning to remove the majority of HFO-generating brain tissue would result in a seizure-free outcome. Additionally, the researchers sought to determine whether fewer surgical resections were associated with greater incidences of poor seizure outcome. During a 1-year study period, a total of 52 patients were included in the analysis. Ripples (80-250 Hz) and fast ripples (250-500 Hz) were also included in the study, with chronic intracranial EEG detecting these variables during slow-wave sleep.

Removal of HFO-generating regions was associated with attainment of a seizure-free outcome at the group level. The investigators observed no association between removal of HFO-generating regions and seizure-free outcome for the center-specific analysis. HFOs were predictors of good or poor surgical outcome in 69.2% (n=36) of patients, resulting in a modest validation of the researchers’ hypothesis. In all centers, surgical outcome was associated with the removal of regions with the highest ripple (S = 15,113.02; P =.044; ρ = −0.32) and fast ripple counts (S = 15,419.5; P =.03; ρ = −0.34).

“HFOs were not better in identifying seizure onset compared to spikes in individual patients, contrary to what had been found in group-level studies,” the researchers wrote. “The current results may therefore be limited to our specific patient groups. Nevertheless, the results question the value of HFOs as biomarkers of epileptic tissue, at least when combined from different centers, different age groups, and different techniques.”